The present invention relates to enhanced roaming of mobile stations in cellular and PCS systems. This invention offers a subscriber the ability to use his/her wireless phone or handset, on its most desirable roaming system in any geographic location, without concern for different service providers or air interface technologies. Intelligence in the network (most particularly at the Home Location Register, HLR), as specified in this invention, will always direct the mobile to access and acquire the most favorable system whenever the subscriber is roaming outside his/her home service market.
One of the most important and distinguishing features of wireless communications is the ability of the mobile station to roam between systems. While roaming, a mobile station typically will select a system made available by a cellular provider in the geographic area where the subscriber is roaming based on its custom system selection method, which emphasizes finding a system (any system) for service. The draw back of this prior approach is that the mobile station does not have any knowledge whether the selected system is the most desirable system, in the sense of whether a more preferred system in a given market (geographic location) may exist for providing better service in terms of roaming rate and compatible services. This makes roaming between systems a big concern from the end user""s perspective, which in the past has directly impacted the growth of the wireless market.
With the introduction of PCS, at any given geographical location, there could eventually be eight wireless systems providing services. Two of them would of course be cellular A-side and B-side service providers at the 800 MHz range. The other six are new comers (Blocks A, B, C, D, E, and F) operating at the 1.9 GHz spectrum. In addition, there are two other factors that have contributed to further confusing the roaming situation even further:
1) In this growing market place, more and more preferred roaming agreements will be established between different service providers in different geographic markets. Considering the fact that today, there are 306 Metropolitan Service Areas MSAs and 428 Rural Service Areas RSAs (each MSA or RSA having 2 cellular operators), and 543 MTAs (Major Trading Area) and BTAs (Basic Trading Area). Each region or area may have up to 6 PCS operators. Because of this large number of operators in the US, the number and level of preferred roaming agreements could soon become overwhelming. With the enactment of the US Telecommunications Act in 1996, more and more alliances and mergers of service providers in the market place are predicted. This creates further confusion to the mobile station as to how it can select a system while roaming having a preferred agreement with its home service provider.
2) With the auction of the PCS spectrum, some service providers now own different segments of the air spectrum in different geographic locations. It is then imperative for mobile stations to be able to access systems provided by the same service provider in different geographic markets to get preferred rates and to preserve the services that the subscriber has with its home base system.
In short, competition in wireless services and service provider""s desire to offer seamless roaming will make the wireless market place more dynamic and vibrant, which in turn impacts the mobile station""s ability to select a favorable system. It is the purpose of this invention to develop a new method, which relies on the intelligence in the network (particularly the Home Location Register, HLR), to guide the mobile station to a preferred cellular provider in any market into which it roams.
In Cellular mobile operation, the mobile station is programmed by either the operator or the end user to scan the spectrum in a pre-defined sequence to find the home service system. For example, if a mobile""s home system is provided by a B-side operator, the mobile station will always scan the B-side channels first when it is turned on, NO MATTER WHERE THE MOBILE IS. If a B-side service provider is not available in the geographic market into which the mobile station has roamed, then, depending upon the pre-defined sequence, the mobile may scan the A-side, or indicate that no service is available in that particular market. It was not heretofore defined in either the standards or in the mobile custom scanning method, for the mobile station to intelligently look for a preferred system that is going to provide the mobile the best service, in terms of the roaming charge, and other factors.
In PCS communications, the way the mobile acquires a system is even more complicated because of the fact that there are up to 6 different. spectrums available, and there are multiple air interfaces. Also, because of the fact that there are microwave interference sources within the PCS spectrum, the frequencies (channel numbers) of pilot channels are not even specified in the standards. For example, in CDMA, there is only a list of candidate channels for the mobile to scan. Given the standardized CDMA system acquisition time of up to 15 seconds to acquire a pilot channel, it is highly impractical for the mobile to scan on its own trying to find the best system in a particular geographic location (i.e., a foreign market).
Even though today the CDMA community is trying to define a handset solution to enhanced roaming, based on pre-programmed sequence of scanning by the service providers, it may not work well at all because of the limited precious mobile station memory. Given the overwhelming number of cellular and PCS systems in service, it is hard to imagine how the mobile will be able to be programmed with information as to preferred systems in all markets. Furthermore, due to the dynamic nature of the wireless market, a handset solution will require periodic updating to provide needed preferred system information. But, updating the list in the mobile has to be originated by the mobile. Considering the fact that the mobile user will have no easy way of knowing that any change in the market place has occurred, this will create nuisance to both the service providers and the end users and is likely to result in unneeded update requests from roaming mobile stations.
In this invention, we describe a network based solution for the purpose of enhanced roaming, namely, the Network Directed System Selection (NDSS) approach. The Network Directed System Selection feature is a network capability that provides a network based mechanism for a service provider, based on various customer and service provider specified criteria, to automatically direct a user to a desired system. The desired system could be any system available to the subscriber unit, regardless of frequency band (cellular A/B or PCS bands A/B/C/D/E/F) or technology (analog or digital).
The Network Directed System Selection (NDSS) feature consists of features that allow a cellular or PCS service subscriber to register upon a preferred system while they are roaming (i.e., outside of their home system) without any manual intervention by the subscriber. NDSS allows a subscriber unit to be automatically directed by their home service provider to a suggested system, regardless of the frequency band (e. g. cellular A/B or PCS bands A/B/C/D/E/F), and be compatible to the air interfaces supported by the terminal. The NDSS feature also allows a network operator to control access to systems to facilitate testing, load control, and service quality control. For example, when a customer registers on a system, the network may direct the user from that system to another system. The subscriber unit may then remain on the system until power down, or until directed back to the original system by a subsequent message from the NDSS feature, or until handed off to another system. NDSS also allows the subscriber to suppress or desuppress the feature.